The invention relates to a rotor disk (1) to be inserted into a receptacle (2) for the treatment of polymers, having a disk body (3) on whose top side (4) mixing and/or comminuting tools (5) are providable and on whose opposite underside (6) a number of conveying ribs (7) extending from the interior to the exterior are provided with which during operation polymer particles are transportable towards the exterior or, respectively, that during operation exert a force directed from the center (8) of the rotor disk (1) towards the exterior on the polymer particles grasped by the conveying ribs (7). In accordance with the invention it is provided that the conveying ribs (7) are curved concavely in the direction of rotation or, respectively, of movement.
Rotor disks in various designs have been known from the state of the art. They are most often arranged near the bottom of a receptacle or, respectively, of a cutter compactor for the processing and conditioning of thermoplastic polymers and essentially consist of a disk-shaped tool carrier at whose top side mixing or, respectively, stirring tools or comminutors are arranged. During operation, the disk revolves and the tools will grasp and, if necessary, comminute the synthetic material fed into the container while simultaneously heating it. In addition, the material is being stirred and constantly moved to the effect that a mixing vortex will form in the container.
In general, devices for the processing of polymers have also been known from the state of the art, for example from AT 375 867 B, AT 407 970 B or WO 93/18902. Due to the revolving tool carriers or, respectively, the tools, the treated synthetic material is hurled against the lateral wall of the container through the effect of centrifugal force. A portion of the synthetic material rises up along the lateral wall of the container and revolves in the form of a mixing vortex but will ultimately fall back into the center of the container. This will result in the desired retention time of the treated synthetic particles in the receptacle so that the synthetic material fed into it will be thoroughly mixed, sufficiently heated by the friction forces and, in the case of tools acting in comminuting fashion on the synthetic material, sufficiently comminuted.
However, it has shown that not the entire amount of synthetic material hurled against the lateral wall of the container rises up on said wall but that a portion will end up below the lowest tool or, respectively, below the lowest disk forming the tool carrier. There, the synthetic portion may fuse in uncontrolled fashion due to the friction effect.
Attempts have been made to avoid this disadvantage through the attachment of conveying ribs to the underside of this disk. From the state of the art, it has been known with regard thereto to attach to the underside of the disk or, respectively, of the tool carrier straight and radial ribs that serve to transport any synthetic material that ends up between the bottom of the cutter compactor and the underside of the tool carrier back towards the exterior and to remove it again from that area.
However, this measure has not been entirely satisfactory. In particular in the case of large-dimensioned receptacles and a correspondingly great filling volume of several hundred kilograms of polymer material, correspondingly large disks with large diameters must be employed. These disks must, on the one hand, be manufactured with great precision and also rotate very quietly and regularly since the distance between the disk and the bottom amounts to only a few millimeters. In such large-dimensioned cutter compactors, great demands are made on the transportation effect of the ribs since, as mentioned before, a great amount of material to be treated is present in the container that, on the one hand, is to be moved and that, on the other hand, exerts great downward pressure due its great own weight, forcing itself into the space between the disk and the bottom.
During the upscaling of such devices it has shown that the conveying capability of the known disks that work sufficiently in the case of small containers will no longer suffice in the case of large containers in order to keep the material away from the problem area. Nor can the rotational speed of the mixing tools used to give the material an upward movement and to increase the retention time be increased at will since due to the generated friction, more heat would be produced that could lead to a local fusion of the flakes.
Again and again, polymer flakes will then end up in the exterior area between the bottom and the disk and remain there permanently. This will increase the temperature in this area, the flakes will agglomerate, becoming gluey and possibly melting, leading to even more flakes accumulating. After some time, the disk will begin to rattle and ultimately jam. Therefore, it is desirable that in the event that at some time a particle does become wedged between the ribs and the container bottom, this particle will be swiftly freed and subsequently be effectively removed again from the critical area.
Moreover, not only larger flakes but also smaller dust particles end up in the critical area below the disk, with the dust particles penetrating even further in the direction of the center of the disk and remaining there. These fine polymer particles will then be heated too much as well and be isolated and caught in the critical area.
In general, this is problematic in the case of disks with a smaller diameter as well since, in particular in the case of heavy grist loads, lower rotational speeds, i.e. relatively low circumferential speeds, are being used.